Two-phase flow in porous media is an important subsurface process that has significant
impacts on the global economy and environments. To study two-phase system in porous
media, capillary pressure (Pc
), relative permeability (Kr), bulk electrical conductivity (σb) and
bulk relative permittivity (εb) are often employed as characterization parameters. Interestingly,
all of these parameters are functions of water saturation (S). However, the non-uniqueness in
the Pc
-S, Kr-S,σb-S and εb-S relationships pose considerable challenges in employing them
for effective monitoring and control of the two-phase flow processes. In this work, laboratory
scale experiments and numerical simulations were conducted to investigate the factors and
conditions contributing to the non-uniqueness in the above relationships for silicone oil-water
and supercritical CO2-water flow in porous media, with a special emphasis on geological
carbon sequestration.
Specifically, the dynamic capillary pressure effect, which indicates the dependence of the Pc
-
S relationship on the rate of change of saturation (∂S/∂t) during two-phase flow in porous
media was investigated. Using a silicone oil-water system, the dynamic capillary pressure
effect was quantified in term of the parameter named the dynamic coefficient,
 , and it was
found to be dependent on the domain scale and the viscosity ratio of the two fluids. It was
found that

increases with the domain scale and the viscosity ratio. It is inversely affected
by
S t
, which is related to the degree of resistance to the fluid motion, namely, viscosity.
In almost all cases,

was found to decrease monotonically with an increase in water
saturation, S. An order increase in magnitude of

was observed as the domain scale
increases from 4cm scale to 8cm in height. A similar order of increase in

was observed in
the 12cm high domain scale. There is an order increase in the value of

for the silicone oilwater
system as the viscosity ratio increases from 200 to 500. For the supercritical CO2
(scCO2) and water system in porous media, the experiments and numerical simulations
showed that

increases with rising system temperature and decreasing porous media
permeability.
Dimensionless analysis of the silicone oil-water experimental results showed that by
constructing non-dimensional groups of quantities expressing a relationship among different
variables on which

depends, it is possible to summarise the experimental results and
determine their functional relationship. A generalised scaling relationship for

was derived
from the dimensionless analysis which was then validated against independent literature
data. The exercise showed that the -S relationship obtained from the literature and the
ii
scaling relationship match reasonably well. This work also demonstrated the applicability of
an artificial neural network (ANN) as an alternative computational platform for the prediction
of the domain scale dependence of
τ .
The dependence of the Kr-S relationship on ∂S/∂t was also investigated. The results showed
that the Kr-S curve under dynamic flow condition is different from that under the quasi-static
condition. Kr
for water (Krw) increases with increasing water saturation and decreases with
the increase in viscosity ratio while Kr
for silicone oil (Krnw) increases with decreasing water
saturation as well as with the increase in viscosity ratio. Also, Krw decreases while Krnw
increases with the increasing boundary pressure.
However, the εb-S and σb-S relationships were found to be independent of ∂S/∂t for the
scCO2-water system in carbonate and silicate porous media. Nevertheless, the εb and σb
values decrease as the water saturation decreases in the two porous media samples. While
εb decreases with increase in temperature in silica sand, the trend in the limestone showed a
slight increase with temperature, especially at high water saturation. Also, the εb-S
relationship is shown to be affected by pressure in silica sand increasing with the pressure of
the domain. On the contrary, the σb-S relationship increases as the temperature increases
with more significance at higher water saturation in the silica sand sample.
This work further demonstrated the application of a membrane in the monitoring of the CO2
in geological sites used for carbon sequestration. Commercial silicone rubber coupled with a
pressure transducer showed potential in the detection of CO2 leakage from geological sites.
The response of the device in terms of the mass of permeated gas, permeability and gas flux
were investigated for both CO2 and N2. In addition, the monitoring of potable water
contamination in a shallow aquifer by the migrating or leaking of CO2 is demonstrated with
the combination of the pH analysis, geoelectrical measurement techniques and the
membrane-sensor system.
Overall, the work in this PhD research demonstrated robust applications of two-phase
systems’ characterization parameters under different scenarios in the porous media.
Implications of the findings in this work to the monitoring and control of two-phase systems in
porous media are expatiated.

Description:

A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.